1. Field of the Invention
The present invention relates to a printing machine such as a printer for a word-processor, type-writer or the like and, more particularly to a control system for press means for pressing a printing paper onto a platen roller.
2. Description of the Prior Art
In a printing machine such as a printer for a word-proccessor, typewriter or the like, there is provided a bail roller for pressing a printing paper onto a platen roller.
As shown in FIG. 1, the bail roller 5 is arranged at leading side of a printing position 1a when seen in a rotational direction of the platen roller 1 as indicated by an arrow X. Usually, it is arranged within a range of one inch in order to make sure the forwarding of a printing paper and to improve a quality of print. As is well known, the bail roller 5 is located at an open position apart from the platen roller 1, as is indicated by a dotted circle, when it is needed to print an area of a blank paper within one inch from the top edge 8a thereof. When an area thereof other than the area mentioned just above is to be printed, the bail roller 5 is closed to press the printing paper onto the platen roller 1 as indicated by a solid line. Namely, the bail roller 5 has to be operated manually from said open position to the press position thereof or vice versa.
In a conventional printer with such a bail roller mentioned above, a jamming is apt to be caused due to the bail roller since the top end of a printing paper is prevented to advance thereby in a case wherein an operator forgot to open it for printing said top area. Also, contrary to the above, when the bail roller is held at the open position, a quality of print is lowered since the printing paper is not held contact onto the platen roller tightly. Further, a possible trouble such as an inclination of the printing paper or a failure in forwarding the same is apt to be caused due to the same reason mentioned above.
In order to dissolve such troubles mentioned above, there has been proposed a printer wherein a blank paper is automatically set at an initial position by operating the bail roller to the open position with use of an operating lever therefor to rotate the platen roller by a predetermined angle. In this case, there may not be caused any trouble as far as the bail roller is so operated as to close to the press position thereof at the timing that the top edge of a printing paper has been advanced from the printing position in a predetermined length which is substantially equal to that of an arc of the platen roller measured from the printing position to the press position of the bail roller. since these operations are controlled sequentially, operational errors are reduced fairly.
However, in this printer mentioned above, it is impossible to print an area within one inch from the top edge of a printing paper, namely an area thereof defined between the bail roller 5 and the printing position 1a.
In order to dissolve this disadvantage mentioned above, there has been proposed a printer wherein the top edge 8a of a printing paper is forwarded to the printing position 1a at first when the bail lever is operated to open the bail roll to the open position and, then, the printing operation is started. When the top edge of the printing paper is forwarded by a predetermined length, the bail roller is automatically closed to press the top end portion of the printing paper onto the platen roller.
However, in this printer, if the platen roller is rotated in a reverse direction and the top edge has been drawn back from the position where the platen roller is contact with the bail roller, the printing paper might be jammed due to the rotation of the platen roller in a normal direction since the bail roller is kept at the closed position thereof.